The present application relates to integrated power, and more particularly to integration of complete switching circuits.
Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art.
The phenomenal increase in power demands of many electronic applications such as computing and telecommunications are driving rapid developments in semiconductor components for power conversion. Recent progress in power device technology has enabled the widespread use of distributed dc power management systems. These architectures offer the advantage of delivering several regulated localized supply rails with ease and the flexibility of selective subsystem shutdown. Power is supplied via a main power bus from an ac-to-dc converter or battery and feeds a number of dc-to-dc converters. Switch-mode dc-to-dc converters provide higher efficiencies, particularly where a low output-to-input voltage ratio results from the widening gap between modern battery technology output voltages and the operating voltages of future ULSI technology.
A generic simplified synchronous buck converter shown in FIG. 1 includes controller and driver functional blocks 110 and 120 respectively. These operate a power High-Side (“HS”) switch Q1 and a Low-Side (“LS”) (synchronous) switch Q2 to regulate the delivery of charge to the load. In this example a series inductance L and shunt capacitance C are used to provide a desired voltage Vout to a load R, but many other circuit configurations are possible.
FIGS. 2(a) and 2(b) show two different known circuit configurations which combine high-side and low-side switches. In FIG. 2(a) N-channel transistors are used for both the high-side and low-side switches, and in FIG. 2(b) a P-channel transistor is used for the high-side switch and an N-channel is used for the low-side switch.
For some applications it is desirable to integrate the high-side and low-side power switches into a single power component. In many other applications it is desirable to integrate the controller-driver functions plus the high-side and low-side power switches into a single power IC. In addition to the advantages of reduced size, a reduction in the number of external components brings about an expected performance improvement due to the elimination of parasitic inductances and capacitances. This enables switching at higher frequencies. Furthermore, integration of the digital cores, analog, and power devices into a single IC enables the design of a complete dc-to-dc converter system using only few external components and lower cost.
The present inventors have proposed, in copending applications, improvements for both vertical and lateral power MOSFET structures, in which the switching performance is improved by incorporating fixed or permanent electrostatic charges. For example, in the device shown in FIG. 3(a), permanent positive charge (QF) 322 is incorporated in trenches 320 filled with a dielectric material such as silicon dioxide. This provides immobile net electrostatic charge. This can be done, for example, by angle-implanting Cesium ions into a thin oxide layer before the trench is filled. The permanent charge shapes the electric field at reverse bias and results in a higher breakdown voltage. In the on-state the permanent charge forms an induced electron drift region in a power MOSFET by forming an inversion layer along the interface between the oxide and P layer. By making use of this new concept a small cell pitch and high packing density can be realized to reduce the device total on resistance.
The circuit combination of a high-side switch in series with a low-side switch, which permits an output node to be connected either to the high-side supply or the low-side supply, is sometimes referred to as a half-bridge or “phase leg.” Integrated phase leg structures have been proposed in, for example, U.S. Pat. No. 6,331,794, which is hereby incorporated by reference.